Human waste disposal in a spacecraft environment is a troublesome issue. Disposal of liquid wastes and of solid wastes has often required separate approaches. In the absence of gravity, feces does not fall away from the body. Use of water to convey feces and control odors, as with standard flush toilets, also requires gravity.
Diapers were used by spacecraft occupants for the earliest missions. Apollo missions used special purpose plastic bags, attached to the user's posterior with an adhesive flange, and finger cots built into sides of bags facilitated transfer of feces. A number of toilets have been built for subsequent Russian and American missions. Most use air flow to convey feces from the body and to control odors. Most collect feces in individual bags; bag walls contain holes or pores to permit air flow while trapping feces.
Diapers and Apollo bags are not user-friendly. Previous toilets have been bulky and heavy. Small spacecraft such as the Apollo capsule or CEV would benefit from a toilet that is user-friendly yet small.
What is needed is a method of processing, sanitizing and storing the remains of human waste during long space flights and similar missions. Preferably, the method should permit separation of most liquids and vapors associated with human waste from the moist solids that are part of such waste.